CBSE Class 10 Biology Heredity Worksheet Set H

ONE MARK QUESTIONS

Question: Mendel observed a contrasting trait in relation to position of flowers. Mention the trait.
Answer: Axial flower position (dominant), terminal flower position (recessive).

Question: How can the chromosomes be identified?
Answer: In human beings, the individual chromosomes are identified by their lengths, position of centromere and banding pattern on staining.

Question: An organism which is a worm, has very simple ‘eyes’, that are really eye spots which detect light. Name that organism.
Answer: Planaria.

Question: What is heredity?
Answer: Transmission of characters and traits from one generation to the next.

Question: All the variations in a species do not have equal chances of survival. Why?
Answer: Some variations are caused by environmental changes and they do not bring out any change in DNA. 
Therefore, all the variations do not have equal chances of survival.

Question: Name the plant on which Mendel performed his experiments.
Answer: Garden pea (Pisum sativum).

Question: Name the term used for the traits that are exhibited externally.
Answer: Phenotype.

Question: No two individuals are absolutely alike in a population.Why?
Answer: All individuals have different kind of DNA. So all individuals are not alike to each other.

TWO MARKS QUESTIONS

Question: “The chromosome number of the sexually producing parents and their offspring is the same”. Justify this statement.
Answer: In sexual reproduction, both the gametes (male and female) contain half the number of chromosomes (haploid or n) and by the fusion of these gametes, the zygote have full set (diploid 2n) chromosomes.

Question: (a) On what rules inheritance is based?
(b) Is each trait influenced by both paternal and maternal DNA?
Answer: a. The rules of inheritance is based on the fact that the traits in the progeny are carried out by DNA’s
of both the parents (mother and father). These rules are known s ‘Mendel’s Laws of Inheritance’.
The rules are:
(i) Law of dominance,
(ii) Law of segregation, and
(iii) Law of independent assortment.
b. Yes, it is true that each trait is influenced by both paternal and maternal DNA.

Question: What is F₂ generation?
Answer: The generation produced by the offsprings of F₁ generation i.e., first generation as parent is called F₂ or second generation.

Question: Variations are important for the survival of species overtime. Justify this statement with reasons.
Answer: a. It causes adaptations,
b. It promotes natural selection.

Question: a. How many gene sets should a germ cell have?
b. Mention two factors causing evolution.
Answer: a. One gene set.
b. (i) Reproduction isolation (ii) Natural selection

THREE MARKS QUESTIONS

Question: “We cannot pass on to our progeny the experiences and qualifications earned during our lifetime”. Justify the statement giving reason and examples.
Answer: Acquiring knowledge / skill in one’s lifetime such as learning dance, music, physical fitness or any other suitable example.
Reason:
a. Such characters / experiences acquired during one’s lifetime do not bring any change in the DNA of the reproducing c$ll/germ cell.
b. Only germ cells are responsible for passing on the characters from the parents to the progeny.

Question: a. Name the scientist who gave the idea of evolution of species by natural selection.
b. What conclusion did Mendel draw from his experiments about traits?
c. Arrange the following according to evolution. Cockroach, Mango tree, Gorilla, Fish
Answer: a. Darwin
b. Traits are inherited independently.
c. Mango tree — Cockroach – Fish — Gorilla.

Question: “Only variations that confer an advantage of an individual organism will survive in a population”. Comment.
Answer: According to Theory of Natural Selection, some variations are advantageous for an organism to adapt better in the prevailing conditions of habitat.
It makes it easy to obtain food and mating partner by them. In this manner they are able to propagate more, transmitting their genes to next generation and producing more individuals with similar genetic makeup and phenotype.
Though according to Genetic Drift Theory, even those not having a variation that confers an advantage also get to 5 survive but only in a small population. If due to an accident most of the individual with other variation get removed, the organisms with leftover variation get to propagate and survive under such circumstances.
Hence it is wrong to say that only variations that confer an advantage of an individual organism will survive in a population.

Question: A pea plant with blue colour flower denoted by BB is cross-breed with a pea plant with white flower denoted by ww.
a. What is the expected colour of the flowers in their F₁ progeny?
b. What will be the percentage of plants bearing white flower in F₂ generation, when the flowers of F₁ plants were selfed?
c. State the expected ratio of the genotypes BB and Bw in the F₂ progeny.
Answer: a. F₁ generation — blue.
b. 25%
c. BB : Bw = 1 : 2.

Question: What is DNA copying? State its importance.
Answer: A process where a DNA molecule produces two similar copies of itself in a reproducing cell.
Importance –
a. It makes possible the transmission of characters from parents to the next generation.
b. It causes variation in the population.

Question: What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Answer: Chromosomes – Thread like structures made up of DNA found in the nucleus. The original number of chromosomes becomes half during gamete formation.
Hence, when the gametes combine, the original number of chromosomes gets restored in the progeny.
(or same thing explained in the form of a flow chart).

Question: Explain Mendel’s concept of heredity, by giving three points.
Answer: a. Mendel worked on pea plant {Pisum sativum) and discovered the fundamental laws of inheritance. He found that traits (characteristics) are controlled by factors (which are now called genes) and each factor (gene) come in pairs. These factors (genes) are inherited as distinct units, one from each parent.
b. Mendel studied that genes segregate during the formation of gametes (sperms in males and ova in females) and they again combine in the offspring (one from each parent) and appear as dominant or recessive trait. This can be worked out by making a test cross.
c. Mendel proposed three laws, namely:
(i) Law of segregation: Each inherited trait is defined by a pair of gene. Parental genes are randomly separated to the germ-cells so that germ contain only one pair of gene.
(ii) Law of independent assortment: Genes of different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.
(iii) Law of dominance: An organism with alternate forms of a gene will express the form that is document.

Question: In a pea plant, find the contrasting trait if:
a. the position of flower is terminal.
b. the flower is white in colour.
c. shape of pod is constricted.
Answer: a. Axial position of flower.
b. Purple colour of flower.
c. Inflated shape.

FIVE MARKS QUESTIONS

Question: (a) Which type of organs are shown in the figure below? 
(b) Which type of origin and structure do these organs have?
Answer:
a. These are organs which help in flying (wings of insects and wings of birds).
b. The structure and components of these wings are different. They look similar because they have a common use for flying, but their origins are not common, i.e., they are analogous.

Question: Give reasons for the following:
a. Traits acquired during lifetime of an individual are not inherited.
b. All the human beings belong to a single species.
c. Variations keep on accumulating during reproduction and do not disappear in next generation.
Answer:
a. These are acquired traits that do not make any change to the DNA of an organism.
b. Homo sapiens originated in Africa and spread across the globe in stages. The humans with different colours in different regions have come into being as an accident of evolution, so that they could live their lives the best they could. So all belong to the same species.
c. Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. So the changes keep on accumulating generations after generations.

Question: Explain with an example for each, how the following provides evidences in favour of evolution in organisms:
a. Homologous organs
b. Analogous organs
c. Fossils
Answer:
a. Homologous organs – study of homologous organs suggests that the organs having same structure but performing different functions have evolved from a common ancestor. Example: forelimbs of a frog, lizard, bird and man.
b. Analogous organs – show adoption of organs for common use. Example: wings of butterfly and wings of bat.
c. Fossils – provide the missing links between two species. Example: – Archeopteryx / fossils of some dinosaurs with feathers.

Question: a. State any two factors that could lead to the rise of a new species.
b. How do analogous organs provide evidence in favour of evolution?
Answer: 
a. Natural Selection, Genetic drift, Mutations,Variations.
b. The organs which are similar in function but are structurally different suggest that although these two organs may look alike superficially giving an idea of common ancestory but the different in structure and origin suggests that organisms having these organs have a distant ancestor but such organs have developed during the course of evolution as an adaptation to similar mode of life.

Question: Variation is useful for the useful over long time. But the variants have unequal chances of survival. Explain this statement. 
or
Define variation in a species. How does it increases the survival chances of a species?
a. Identify the organism shown in the above figure.
b. Name one incipient feature selected by the nature.
c. Mention any other primitive feature of birds.
Answer: Variation are minor differences among members of a population. They are useful for the process of evolution which take place over long time. But some of the variants find it more advantageous in the present environmental conditions to survive than others variants by virtue of the variation possessed by them hence they have unequal chances of survival. Thus some get selected and others get eliminated. Those which survive pass their genes to next generation therefore frequency of genes possessed by them increase in frequency in the population. Example – in a population of beetles, a new variation (green colour) get survival benefit/advantage to green beetles whereas other (red) perishes.

Question: If a population of red beetles, living on green bushes, is being eaten by crows. During sexual reproduction,
a green beetle is found in progeny:
a. What is the future of new trait?
b. Will it survive in the new habitat?
Answer:
a. Among progeny, when green beetle is found, it escaped attack of crows as it merged with green colour. Green beetles increased, red decreased.
b. New trait will survive.

Question: With the help of suitable examples, explain why certain traits cannot be passed on to the next generation. What are such traits called?
Answer: Example: Acquiring knowledge by reading/change in body weight. Reason: Because such changes do not bring any change in the DNA of the germ cells/such changes take place only in the non-reproductive tissues.
Traits: Acquired traits.

Question: (a) Differentiate between:
1. Homologous organs and Analogous organs.
2. Pollination and Fertilization
(b) What do fossils tell us about the process of evolution?
Answer:
a. (i) Organs in different organisms with same origin with different function/ different origin, same function.
(ii) Transfer of pollen from the stamen to the pistil of the flower/fusion of male and female gametes.
b. Help in establishing links and act as evidence of evolution.

Question: An organ like a wing in birds are an advantage to an organism. Did they appear in different stages or were formed due to a single sudden change in them.
Answer: 
Feathers in dinosaur were long and they could not fly using feathers. It gave them protection from cold weather and warmth. Birds seem to have later adapted the feathers to flight.

Question: How green beetles had colour advantage over red beetles? Explain.
Answer: Green beetle merge with green background of vegetation which give survival advantage to a species from elimination.
a. in the population of beetles, the new variation (green colour) get survival benefit / advantage to green beetles whereas other (red) perishes.
b. It is because of Natural selection — some variations are advantageous for an organism to adapt better in the prevailing conditions of habitat. It makes it easy to obtain food and mating partner by them.
In this manner they are able to propagate more, transmitting their genes to next generation and producing more individuals with similar genetic makeup and phenotype.

Question: Fore limbs of amphibians, reptiles, birds and mammals show similarity in their bones but Wings of bat and bird don’t. What conclusion can be drawn from such observation regarding their ancestry?
Answer: The organs which have similar basic structure and mode of origin but perform different functions in different animals are called homologous organs, e.g.,forelimbs of amphibians, reptiles, birds and mammals.
Homologous organs give an evidence of common ancestory and evolutionary relationship between apparently different species.
Analogous organ are the organs in different organisms which have different basic structure but have similarity in shape and function, e.g., wings of bat and bird. These organs do not provide an evidence in support with common ancestory.

Question: “We cannot pass on to our progeny the experiences and qualifications earned during our lifetime”. Justify the statement giving reason and examples.
Answer:
Acquiring knowledge / skill in one’s lifetime such as learning dance, music, physical fitness or any other suitable example.
Reason:
a. Such characters / experiences acquired during one’s lifetime do not bring any change in the DNA of the reproducing c$ll/germ cell.
b. Only germ cells are responsible for passing on the characters from the parents to the progeny.

Question: Discuss the role of variations in evolution. What is natural selection and genetic drift? 
or
Explain the following:
(a) Speciation (b) Natural Selection
Answer:
a. The members of a population have minor differences among them which is called variations.
b. Two sources of variations are sexual reproduction and environmental factors.
c. Sexual reproduction has greater chances of producing variation.
d. Variations with some advantage has greater chances of surviving, for example, long neck of giraffe.
e. Natural selection and genetic drift lead to formation of new species hence evolution.
Natural Selection: Some variations may have survival advantage hence they happen to gain over others so that they can propagate more than others. Ultimately such variations are selected and propagated among all members of the population. 

This is called adaptation of the species which help them to cope well in their surroundings.
In course of time, it could lead to accumulation of adaptation. In geographically separated populations of a species and development of reproductive barrier among them may lead to the formation of a new species.
Genetic Drift: Some variation may not give survival advantage to members of population.
But if by chance other variations are wiped out from populations, the remaining variations get propagated in next generations.

Question: Rekha is very dark in colour. She stays very quiet at home and in her class also. She is always seeing for the beauty products which can help her to become fair. Her friend Lila talks to her about excessive use of beauty products and tells her that they are very harmful and colour comes by birth and she is not responsible for her dark colour.
a. What might have caused Rekha’s colour to be dark?
b. Is it possible that all the family members of Rekha’s family were dark?
c. What value do you learn?
Answer: 
a. Her dark colour may be due to the genetic inheritance.
b. All may not be dark, depending upon the genes inherited and the environmental conditions that each one of them living in.
c. Awareness, logical thinking, scientific temperament.

Question: (a) Identify the organism shown in the above figure. (Image 85)
(b) Name one incipient feature selected by the nature.
(c) Mention any other primitive feature of birds.
Answer:
a. Planaria.
b. Eyes which were there only for detecting light.
c. Birds developed feathers for insulation.

Question: Explain the term homologous organ with an example.
Answer: The organs which have similar basic structure and mode of origin but perform different functions in different animals are called homologous organs. E.g., Forelimbs of amphibians, reptiles, birds and mammals.
Homologous organs give an evidence of common ancestory and evolutionary relationship between apparently different species.

Question: a. Why traits such as intelligence and knowledge cannot be passed on to the next generation?
b. How can we say that birds are closely related to reptiles and have evolved from them?
Answer: a. Traits such as intelligence and knowledge are not heritable traits, which do not bring upon any changes in the DNA of the germ cells and, therefore, cannot be passed on to the progeny.
b. This can be said because traits such as feathers were first seen in reptiles like Dinosaurs, which performed the function of providing insulation to them in cold weather although they could not fly using the feathers but later birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptiles.

Question: Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.
Answer: Evolution is the formation of more complex organisms from pre-existing simpler organisms over a certain period. Accumulation of variation in genetic material forms the basis of evolutionary processes.
Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history.
Importance of fossils in the evolutionary process:
a. Some invertebrates living on the sea bed died and were buried in the sand.
b. More sand was accumulated and formed ,sandstone under pressure.
c. After millions of years, dinosaurs living in the area died and their bodies were buried in the mud.
d. The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils.
e. Again millions of years later, the bodies of horselike creatures dying in the area were fossilised in the rocks above the earlier rocks.
f. Much later, because of erosion and water flow, some rocks wore out and exposed the horse-like fossils.